JP3100729B2 - Magnetostrictive displacement detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetostrictive displacement detecting apparatus for detecting a mechanical displacement of an object or a displacement of a liquid surface by using a magnetostrictive phenomenon.

[0002]

2. Description of the Related Art Heretofore, as a magnetostrictive displacement detecting device, the present applicant has applied a current pulse to a magnetostrictive wire so that a torsional elastic wave (a torsional elastic wave) is generated at a portion of the magnetostrictive wire close to a permanent magnet movable along the magnetostrictive wire. (U.S. Pat. No. 6,097,045), which detects the mechanical displacement applied to a permanent magnet by generating ultrasonic waves and measuring the propagation time of a torsional elastic wave to a receiver provided at a specific portion of the magnetostrictive wire. 61-112923, JP-A-63-217224). As the receiver,
A device in which a touch element is brought into contact with the magnetostrictive wire almost perpendicularly, converts the torsional elastic wave into an axial force of the touch element, and detects the arrival of the torsional elastic wave using a piezoelectric element attached to the end of the touch element. Also, there is a coil that uses a reverse magnetostriction effect (Villari effect) to detect the arrival of a torsional elastic wave propagated through a magnetostrictive wire in a non-contact manner.

[0003]

In order to improve the detection accuracy and reliability of this type of displacement detecting device, noise in the detected waveform received by the receiver should be reduced and a large waveform can be obtained. Need to be In order to obtain a large detection waveform, measures such as increasing the current pulse, increasing the magnetic force of the permanent magnet, or increasing the gain of an amplifier that amplifies the output of the receiver may be used. However, when the current pulse is strengthened, there are problems such as an adverse effect of noise on the circuit and an increase in current consumption. Further, there is a limit in increasing the magnetic force of the permanent magnet, and there is a disadvantage that a permanent magnet having a strong magnetic force is expensive. Further, when the gain of the amplifier is increased, there is a disadvantage that noise included in the detected waveform is also amplified accordingly. Further, in order to reduce noise in the detected waveform, a method of covering the magnetostrictive wire or the outside of the receiver with multiple layers with a shield material, or electrically removing noise in the detected waveform with a filter or the like is used. However, there are problems that the device becomes large and the circuit becomes complicated. SUMMARY OF THE INVENTION It is an object of the present invention to provide a magnetostrictive displacement detecting device which can obtain a significantly larger detected waveform with a very simple configuration than in the past.

[0004]

In order to achieve the above-mentioned object, the present invention provides a method in which a current pulse is applied in the axial direction of a magnetostrictive wire so that a permanent magnet that can move along the magnetostrictive wire is moved in proximity to the magnetostrictive wire. A device for generating a torsional elastic wave at a site and measuring a propagation time of the torsional elastic wave to a receiver provided at a specific portion of the magnetostrictive wire to detect a mechanical displacement applied to the permanent magnet; Is composed of two permanent magnets that move integrally along the magnetostrictive line. The two permanent magnets are connected to each other so that the peaks or valleys of the torsional elastic wave generated by these permanent magnets overlap. They are arranged at regular intervals in the axial direction.

[0005]

The present inventor conducted experiments on the waveform of torsional elastic waves using a plurality of permanent magnets. As a result, when the two permanent magnets were brought close to a certain distance in the axial direction of the magnetostrictive wire, the torsion generated by both permanent magnets was measured. They have discovered that elastic waves overlap and cause resonance or similar phenomena, with the amplitude being greater than the sum of the amplitudes of the original waveforms. Note that when the two permanent magnets are brought closer to each other than the above distance, the amplitude of the waveform becomes smaller. By using two permanent magnets in this way, the current pulse can be increased, the magnetic force of the permanent magnets can be increased,
Alternatively, a detected waveform having a large amplitude can be obtained without taking measures such as increasing the gain of an amplifier that amplifies the output of the receiver.

[0006]

FIG. 1 shows an example of a magnetostrictive displacement detecting device according to the present invention. The start end of the magnetostrictive wire 1 is clamped by a clamp member 3 fixed on a base 2, and the end is supported by a support member 5 via a spring 4. Therefore, a constant tension is always applied to the magnetostrictive wire 1. In addition,
A damping material 6 such as silicon rubber is provided at the end of the magnetostrictive wire 1.
Is applied, and the influence of the reflected wave from the spring 4 or the support member 5 is suppressed. The receivers 7 and 8 are arranged near the clamp member 3 and have a built-in coil 7.
A magnetostrictive wire 1 penetrates through the central portions of a and 8a without contact.
The coils 7a and 8a are composed of coils having the same characteristics, are arranged at a distance L in the axial direction of the magnetostrictive wire 1, and detect a torsional elastic wave propagating through the magnetostrictive wire 1 by utilizing the inverse magnetostrictive effect. Since the negative electrodes of the coils 7a and 8a are grounded and the positive electrodes are connected to the positive and negative inputs of the differential amplifier 9, respectively, both coils are connected in opposite phases. Two permanent magnets 10 and 11 shown in FIG. 2 are inserted through the magnetostrictive wire 1 so as to be movable in the axial direction, and the permanent magnets 10 and 11 are spaced at a predetermined interval M by a cylindrical holder 12 made of a non-magnetic material. Has been held. This interval M is set to about 19 mm as described later. The permanent magnets 10 and 11 of this embodiment are ring-shaped ferrite-based permanent magnets having N poles on the inner periphery and S poles on the outer periphery.

A current pulse is supplied from a pulse generator (not shown) to the beginning of the magnetostrictive wire 1 protruding from the clamp member 3, and the end of the magnetostrictive wire 1 is returned to the ground of the pulse generator via a spring 4. Therefore, the receivers 7, 8
In this case, torsional elastic waves generated by the permanent magnets 10 and 11 are detected. The detected waveform differs depending on the distance L between the two receivers 7 and 8. In this embodiment, the distance L is set to the peak of the front waveform received by the receiver 7 and the rear peak received by the receiver 8. The distance is set to exactly overlap the first peak of the waveform. Therefore, a waveform larger than the waveform obtained by a single receiver is obtained at the output of the differential amplifier 9. In addition, more information on this patent the applicant has already submitted application (Japanese Patent Application No. 3
356948) .

FIGS. 3 to 6 show examples of detected waveforms output from the differential amplifier 9 when the two permanent magnets 10 and 11 are arranged at intervals in the axial direction of the magnetostrictive wire 1. FIG. The shape of the permanent magnets 10 and 11 is 16 mm in inner diameter and 2 mm in outer diameter.
It is 2 mm and 4 mm thick. FIG. 3 shows two permanent magnets 1
0 and 11 are 100 mm apart, and are detected as two independent waveforms 13 and 14. FIG. 4 shows a case where the distance between the permanent magnets 10 and 11 is reduced to 30 mm, and the front and rear waveforms 13 and 14 appear in a partially overlapped state. Therefore, it is difficult to distinguish two waveforms.
FIG. 5 shows a case where the interval between the permanent magnets 10 and 11 is reduced to 19 mm, and the two waveforms overlap each other to form a waveform 15 having the maximum amplitude. The peak 15 a of the peak of the waveform 15 is 2.74 times the peak 13 a of the peak of the original waveform 13,
The valley peak 15b is the valley peak 13b of the original waveform 13.
2.42 times the amplitude of FIG. 6 shows permanent magnets 10 and 1
This is a case where the interval of 1 is reduced to 13 mm, and the waveform 16 has a smaller amplitude than the original waveforms 13 and 14.

FIGS. 7 and 8 show the results of experiments in which N poles and S poles are magnetized on both end faces as permanent magnets 20 and 21, respectively, and the N poles face the receiver. The other conditions are the same as those in FIGS. FIG. 7 shows two permanent magnets 20,
21 are 100 mm apart, and are detected as two independent waveforms 22, 23. FIG. 7 shows a permanent magnet 20,
In this case, the interval of 21 is reduced to 19 mm, and the two waveforms 22 and 23 overlap each other, and the waveform 24 has the maximum amplitude. The peak 24a of the peak of the waveform 24 has an amplitude 3.11 times the peak 22a of the original waveform 22, and the peak 24b of the valley of the waveform 24 has an amplitude 2.54 times the peak 22b of the valley of the original waveform 22. . The permanent magnets 20, 21
Is smaller than 19 mm, the amplitude becomes smaller as in FIG.

FIGS. 9 and 10 show a permanent magnet 30 having an N pole on the inner circumference and an S pole on the outer circumference, and a permanent magnet 31 having N poles and S poles on both end faces. This is an experiment result in which the magnet 30 was arranged on the receiver side and the S pole of the permanent magnet 31 was arranged so as to face the permanent magnet 30 side. The other conditions are the same as those in FIGS. FIG. 9 shows a case where the two permanent magnets 30 and 31 are separated by 100 mm, and are detected as two independent waveforms 32 and 33. FIG. 9 shows a case where the interval between the permanent magnets 30 and 31 is reduced to 10 mm, and the two waveforms 32 and 33 overlap to form a waveform 34 having the maximum amplitude. The peak 34 of the mountain of this waveform 34
“a” has an amplitude of 3.21 times the peak 32 a of the original waveform 32 and a peak 34 b of the valley of the waveform 34 has an amplitude 2.54 times the peak 32 b of the valley of the original waveform 32. The permanent magnet 3
When 0 and 31 are set closer than 10 mm, a waveform having a small amplitude is obtained as in FIG.

FIG. 11 shows the permanent magnet 3 shown in FIGS.
The arrangement of 0, 31 is reversed, that is, the permanent magnet 31 is arranged on the receiver side, and the S pole of the permanent magnet 31 is
It is an experimental result arranged so as to face the side. The other conditions are the same as those in FIGS. Also in this case, the waveform 35 has the maximum amplitude when the interval between the permanent magnets 30 and 31 is 10 mm. The peak 35a of the peak of the waveform 35 has 3.21 times the amplitude of the peak 32a of the original waveform 32, and the peak 35b of the valley of the waveform 35 has 2.65 times the amplitude of the peak 32b of the valley of the original waveform 32. .

As is apparent from the above experimental results, when two permanent magnets having the same magnetization direction are used (FIGS. 5 and 8), the maximum waveform is obtained when the interval between the permanent magnets is set to about 19 mm. And the amplitude of the waveform is more than twice the original waveform. On the other hand, when two permanent magnets having different magnetization directions are combined (FIGS. 10 and 11), the amplitude of the waveform is larger than when the permanent magnets having the same magnetization direction are used (FIGS. 5 and 8). Is further increased, and the set distance between the two permanent magnets is also reduced to 10 mm, which is the most desirable for the displacement detection device.

The mechanical displacement x applied to the permanent magnet
Can be easily obtained by a known method. That is, the displacement x of the permanent magnet is obtained by the following equation from the time t from the supply of the current pulse to the arrival of the torsional elastic waves at the receivers 7 and 8 and the propagation velocity v of the torsional elastic waves of the magnetostrictive wire 1. Can be. x = v · t Further, the propagation velocity v and the circuit section are affected by the temperature change, and therefore, an error may also occur in the measured displacement x. In order to eliminate such an error, a fixed permanent magnet may be arranged at a predetermined position in addition to the movable permanent magnet, and the displacement x may be obtained from a ratio of the propagation times or a difference in the propagation times.

The above embodiment is merely an example of the present invention, and can be modified without departing from the spirit of the present invention. In the above embodiment, a receiver having two coils connected in opposite polarities was used to obtain a large detection waveform. However, a single coil may be used instead. Alternatively, the torsional elastic waves may be converted into the axial force of the tentacle, and the arrival of the torsional elastic wave may be detected by a detector such as a piezoelectric element attached to the end of the tentacle. When the polarities of the two coils are connected in reverse, a differential amplifier is used in the embodiment. However, the positive and negative electrodes of the two coils are connected to each other, and the remaining two poles are taken out as outputs. It may be. Further, in the above embodiment, a solid line is used as the magnetostrictive line,
Although an example in which a current pulse is directly supplied to this magnetostrictive wire has been described,
As described in JP-A-59-162412, a configuration may be adopted in which the magnetostrictive wire is formed in a tube shape, and a conductor for flowing a current pulse is inserted into the center of the magnetostrictive wire. The permanent magnet used in the present invention is not limited to the annular shape as in the embodiment, but may be any shape such as a rectangular parallelepiped or a U-shape. Although the waveform of the torsional elastic wave varies depending on the shape and the magnetization direction of the permanent magnet, the same effect as the present invention can be exerted by arranging two permanent magnets at a predetermined interval.

[0015]

As is apparent from the above description, according to the present invention, the two permanent magnets are arranged at a fixed distance in the axial direction so that the peaks or valleys of the torsional elastic waves overlap. A significantly larger detection waveform can be obtained under the same conditions as in the related art. Therefore, the detected waveform of the torsional elastic wave can be made relatively larger than the noise that enters from the outside,
The S / N ratio can be greatly improved. In addition, the torsional elastic wave attenuates according to the distance from the permanent magnet to the receiver, and attenuates when the temperature rises to near the magnetic transformation point of the magnetostrictive line,
In the past, there were severe restrictions on the measurement length and the upper limit temperature of use, but in the present invention, the amplitude of the torsional elastic wave can be increased, so that the measurement length can be longer than before and the upper limit temperature of use can be increased Becomes

[Brief description of the drawings]

FIG. 1 is a schematic layout diagram of a magnetostrictive displacement detection device according to the present invention.

FIG. 2 is a sectional view of a holder holding a permanent magnet.

FIG. 3 is a detection waveform diagram of the first embodiment when two permanent magnets are separated by 100 mm.

FIG. 4 is a detection waveform diagram of the first embodiment when two permanent magnets are brought close to 30 mm.

FIG. 5 is a detection waveform chart of the first embodiment when two permanent magnets are brought close to 19 mm.

FIG. 6 is a detection waveform diagram of the first embodiment when two permanent magnets are brought close to 13 mm.

FIG. 7 is a detection waveform diagram of the second embodiment when two permanent magnets are separated by 100 mm.

FIG. 8 is a detection waveform diagram of the second embodiment when two permanent magnets are brought closer to 19 mm.

FIG. 9 is a detection waveform diagram of the third embodiment when two permanent magnets are separated by 100 mm.

FIG. 10 is a detection waveform diagram of the third embodiment when two permanent magnets are brought close to 10 mm.

FIG. 11 is a detection waveform diagram of the fourth embodiment when two permanent magnets are brought close to 10 mm.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Magnetostrictive wire 7, 8 Receiver 7a, 8a Coil 9 Differential amplifier 10, 11 Permanent magnet 12 Holder

──────────────────────────────────────────────────続 き Continued on the front page (58) Fields surveyed (Int. Cl. ⁷ , DB name) G01B 17/00-17/08 G01D 5/00-5/252 G01D 5/39-5/62

Claims (1)

(57) [Claims] 1. A torsional elastic wave is generated at a portion of a magnetostrictive wire adjacent to a permanent magnet movable along the magnetostrictive wire by flowing a current pulse in an axial direction of the magnetostrictive wire, and provided at a specific portion of the magnetostrictive wire. A device for detecting the mechanical displacement applied to the permanent magnet by measuring the propagation time of the torsional elastic wave to the receiver, wherein the two permanent magnets move integrally along the magnetostrictive line. Wherein two permanent magnets are arranged at regular intervals in the axial direction of the magnetostrictive wire so that the peaks or valleys of the torsional elastic waves generated by these permanent magnets overlap each other. Type displacement detector.